The Present Invention relates to a chuck for holding a graphite electrode during electrode machining and during electrical discharge machining procedures using the previously machined electrode.
Injection molding processes require the production of molds or tooling, which generally comprise two halves. Molds are made of blocks of solid metal, usually high-grade tool steel; however, mold making is a highly sophisticated process and often involves the incorporation into a mold of several different metal alloys. Each of the two mold halves define separate negative depressions that will eventually face each other during the injection molding process. When the two mold halves are clamped together, a cavity is formed which, when filled with pressurized molten plastic or metal from an injection molding press, forms a finished part having the outer dimensions of the cavity defined by the two mold halves.
Building the injection mold or tooling thus requires the creation of depressions in blocks of solid metal. For the finished part to meet quality standards, the depressions must be precisely placed on the mold halves, both as to the three dimensional outer contours of the depression as well as the two dimensional location of the corresponding depressions on the facing surfaces of the corresponding mold halves. Various techniques are used to create mold depressions, both separately and in combination, including traditional machining, CNC machining, EDM techniques and manual techniques. EDM encompasses two-separate techniques, wire EDM and plunge EDM. Plunge or sinker EDM requires mounting to an EDM machine an electrode machined into the shape of half of the desired finished part. The metal block that will be machined into a mold half is placed in the EDM machine and submerged in a dielectric fluid. A servo system advances the electrode into the dielectric fluid toward the metal block. At a point when the electrode is in close proximity with the metal block (i.e., .0.002 inch), an electric field punctures the dielectric fluid and electrical pulses begin to flow. The electrode contacts the metal block and creates sparks with short, intense, pulses of electric energy. Each spark leaves a tiny crater, resulting in the EDM cutting action. The position of the electrode is gradually deepened as metal is removed from the block, eventually resulting in a depression having the exact contours of the machined electrode.
In order for an EDM machine to be able to machine a metal block with sufficient precision, it is necessary for the electrode to be firmly mounted to the EDM machine. Present systems for mounting graphite electrodes to EDM machines include one manufactured by 3R corporation of Stockholm, Sweden. The 3R system involves an electrode mounted to a xe2x80x9ccoinxe2x80x9d by either gluing or screws extending from the coin into the electrode. When the electrode is mounted to the coin, the coin is mounted to a chuck by means of tightening surrounding jaws via set screws. Finally, the chuck is mounted to an EDM or CNC machine. Erowa of Reinach, Switzerland manufactures another system, which features a graphite block mounted to a coin by four screws. The mounted coin is finally mounted to a chuck on an EDM or CNC machine, which requires hand tightening the chuck jaws. Finally, Hirschmann GmbH, Fluorn-Winzeln, Germany, manufactures a coin system for mounting electrodes involving two pins to aid in alignment. All of the above described systems involve relatively lengthy and expensive processes requiring either pre-mounted coins or gluing or screwing the electrode onto coins, followed by hand-tightening the coins to a chuck and sometimes separately mounting a chuck to an EDM or CNC machine. What is clearly needed is a faster and less expensive way to attach to and remove an electrode from an EDM or CNC machine that eliminates the need for a coin system.
A first aspect the invention is a chuck used to mount an electrode to an EDM or CNC machine. A first embodiment of the chuck includes (i) a body with a longitudinal bore, (ii) a draw bar configured and arranged for longitudinal slidable engagement within the bore as between a machining position and a release position, and (iii) a release mechanism in physical communication with the bore whereby activation of the release mechanism is effective for moving the draw bar from the machining position to the release position.
A second embodiment of the chuck includes (i) a body having a mounting surface and a bore longitudinally extending into the body from the mounting surface, (ii) a draw bar configured and arranged for slidable engagement within the bore, and (iii) a release mechanism coupled to the body and in communication with the bore for movement between a first position and a second position wherein the release mechanism is effective for longitudinally lifting the draw bar from a machining position to a release position when the release mechanism is moved from the first position to the second position.
A second aspect of the invention is a combination of a chuck selected from the chucks disclosed above with a graphite workpiece releasably mounted to a first longitudinal end of the draw bar.